Electrosurgical instruments have been used for many years in high-frequency surgery to coagulate or cut biological tissue. With coagulation, a high-frequency current is passed through the tissue being treated, causing it to alter due to protein coagulation and dehydration. Here, the tissue constricts in such a way that the vessels occlude and bleeding is staunched. A high current density is required for a cutting procedure, the effect being that explosive vaporisation of the tissue fluid and tearing of the cellular membranes completely cut the tissue in two.
The use of bipolar instruments is gaining in importance more and more, since lower current strengths than with monopolar instruments are required. It is particularly advantageous that the direction of current between the electrode parts of bipolar instruments can be calculated and does not proceed any distance through the body of the patient.
Bipolar instruments have two articulated squeezing parts and gripping devices are provided at their proximal ends for handling the squeezing parts. At the distal ends of the squeezing parts, there are electrode parts for grasping tissue and for conducting a coagulating current through the tissue. A voltage produced by a HF generator, and the HF current which this provides, is conducted via current-supplying devices to the electrode parts of the bipolar instrument. To prevent a short circuit upon contact of the two electrode parts, the known instruments have a device for preventing a short circuit accommodated on the branches, whereby the electrode parts are always spaced apart when the instrument is closed.
The problem with the known devices for preventing a short circuit is that they only indirectly define the space between the electrode parts, because they are accommodated away from the electrode parts. Thus, the aspect ratios of the branches, for example, need to be taken into account to determine the appropriate space. This makes the adjustment of space and required HF voltage considerably difficult.